This invention relates generally to temperature compensated voltage reference sources, and more particularly to temperature compensated voltage references sources which include Zener diodes.
As is known in the art, voltage reference sources have application in a wide variety of electronic circuits such as analog-to-digital converter circuits and voltage-to-frequency converter circuits, for example. One type of voltage reference source includes a Zener diode, having its breakdown junction formed beneath the surface of a semiconductor layer which provides a portion of an integrated circuit. One such Zener diode is discussed in an article entitled "I.sup.2 L puts it all together for 10-bit a-d converter chip" by Paul Brokaw, published in Electronics, Apr. 13, 1978 on pages 99-105. One special type of such buried Zener diode is a so-called "Kelvin Buried Zener" diode, such diode being characterized by having a sense terminal anode and a force terminal anode in addition to its cathode electrode. As discussed in an article entitled "Circuit Techniques For Achieving High-Speed Resolution A/D Conversion" by Peter Holloway and Michael Timko in the 1979 IEEE International Solid State Circuits Conference, Digest of Technical Papers, pages 136-137, such Kelvin Buried Zener diode has been found to have a temperature coefficient which varies with the processing in a way which correlates with the variation in its Zener breakdown voltage. This relationship was used to provide a temperature compensated buried Zener voltage reference source. In particular, as described in such latter article, the variation in Zener breakdown voltage as a function of temperature was plotted for a number of Zener diodes and it was determined that all curves intersected at a common point or "temperature", T.sub.K. A compensation network was designed to add a voltage, V.sub.COMP, to the Zener breakdown voltage V.sub.Z in such a way that the resulting output voltage, V.sub.0, had a zero temperature coefficient. This was done by making a family of V.sub.COMP versus temperature curves produced by trimming a pair of resistors in the circuit so that the compensation curves had a common intercept at the same point or "temperature", T.sub.K, as the common intercept point of the Zener diodes referred to above. The resulting circuit included the use of a differential amplifier having one input fed by the sense electrode of a Kelvin buried Zener diode (i.e. the voltage V.sub.Z) and a second input fed by the compensating network (i.e. the voltage V.sub.COMP).
While the circuit described in the latter article provides temperature compensation for the buried Zener diode, the circuit is relatively complex in its use of a differential amplifier and further the circuit is limited in the range of obtainable reference voltages.